The present invention is generally directed to a surgical treatment for glaucoma and other eye diseases and relates more particularly to an inflatable device and method for use in ophthalmic surgery to mechanically dilate Schlemm""s canal in the eye and/or instill medications within Schlemm""s canal for direct action upon the canal, the trabecular meshwork, and adjacent tissues.
Glaucoma is a significant public health problem, because glaucoma is a major cause of blindness. The blindness that results from glaucoma involves both central and peripheral vision and has a major impact on an individual""s ability to lead an independent life.
Glaucoma is an optic neuropathy (a disorder of the optic nerve) that usually occurs in the setting of an elevated intraocular pressure. The pressure within the eye increases and this is associated with changes in the appearance (xe2x80x9ccuppingxe2x80x9d) and function (xe2x80x9cblind spotsxe2x80x9d in the visual field) of the optic nerve. If the pressure remains high enough for a long enough period of time, total vision loss occurs. High pressure develops in an eye because of an internal fluid imbalance.
The eye is a hollow structure that contains a clear fluid called xe2x80x9caqueous humor.xe2x80x9d Aqueous humor is formed in the posterior chamber of the eye by the ciliary body at a rate of about 2.5 microliters per minute. The fluid, which is made at a fairly constant rate, then passes around the lens, through the pupillary opening in the iris and into the anterior chamber of the eye. Once in the anterior chamber, the fluid drains out of the eye through two different routes. In the xe2x80x9cuveoscleralxe2x80x9d route, the fluid percolates between muscle fibers of the ciliary body. This route accounts for ten percent of the aqueous outflow. The primary pathway for aqueous outflow is through the xe2x80x9ccanalicularxe2x80x9d route that involves the trabecular meshwork and Schlemm""s canal.
The trabecular meshwork and Schlemm""s canal are located at the junction between the iris and the sclera. This junction or corner is called xe2x80x9cthe angle.xe2x80x9d The trabecular meshwork is a wedge-shaped structure that runs around the circumference of the eye. It is composed of collagen beams arranged in a three-dimensional sieve-like structure. The beams are lined with a monolayer of cells called trabecular cells. The spaces between the collagen beams are filled with an extracellular substance that is produced by the trabecular cells. These cells also produce enzymes that degrade the extracellular material. Schlemm""s canal is adjacent to the trabecular meshwork. The outer wall of the trabecular meshwork coincides with the inner wall of Schlemm""s canal. Schlemm""s canal is a tube-like structure that runs around the circumference of the cornea. In human adults, Schlemm""s canal is believed to be divided by septa into a series of autonomous, dead-end canals.
The aqueous fluid travels through the spaces between the trabecular beams, across the inner wall of Schlemm""s canal into the canal, through a series of collecting channels that drain from Schlemm""s canal and into the episcleral venous system. In a normal situation, aqueous production is equal to aqueous outflow and intraocular pressure remains fairly constant in the 15 to 21 mm Hg range. In glaucoma, the resistance through the canalicular outflow system is abnormally high.
In primary open angle glaucoma, which is the most common form of glaucoma, the abnormal resistance is believed to be along the outer aspect of trabecular meshwork and the inner wall of Schlemm""s canal. It is believed that an abnormal metabolism of the trabecular cells leads to an excessive build up of extracellular materials or a build up of abnormally xe2x80x9cstiffxe2x80x9d materials in this area. Primary open angle glaucoma accounts for approximately eighty-five percent of all glaucoma. Other forms of glaucoma (such as angle closure glaucoma and secondary glaucomas) also involve decreased outflow through the canalicular pathway but the increased resistance is from other causes such as mechanical blockage, inflammatory debris, cellular blockage, etc.
With the increased resistance, the aqueous fluid builds up because it cannot exit fast enough. As the fluid builds up, the intraocular pressure (IOP) within the eye increases. The increased IOP may compromise the vascular supply to the optic nerve that carries vision from the eye to the brain. Some optic nerves seem more susceptible to IOP than other eyes. While research is investigating ways to protect the nerve from an elevated pressure, the only therapeutic approach currently available in glaucoma is to reduce the intraocular pressure.
The clinical treatment of glaucoma is approached in a step-wise fashion. Medication often is the first treatment option. Administered either topically or orally, these medications work to either reduce aqueous production or they act to increase outflow. Currently available medications have many serious side effects including: congestive heart failure, respiratory distress, hypertension, depression, renal stones, aplastic anemia, sexual dysfunction and death. Compliance with medication is a major problem, with estimates that over half of glaucoma patients do not follow their correct dosing schedules.
When medication fails to adequately reduce the pressure, laser trabeculoplasty often is performed. In laser trabeculoplasty, thermal energy from a laser is applied to a number of noncontiguous spots in the trabecular meshwork. It is believed that the laser energy stimulates the metabolism of the trabecular cells in some way, and changes the extracellular material in the trabecular meshwork. In approximately eighty percent of patients, aqueous outflow is enhanced and IOP decreases. However, the effect often is not long lasting and fifty percent of patients develop an elevated pressure within five years. The laser surgery is not usually repeatable. In addition, laser trabeculoplasty is not an effective treatment for primary open angle glaucoma in patients less than fifty years of age, nor is it effective for angle closure glaucoma and many secondary glaucomas.
If laser trabeculoplasty does not reduce the pressure enough, then filtering surgery is performed. With filtering surgery, a hole is made in the sclera and angle region. This hole allows the aqueous fluid to leave the eye through an alternate route.
The most commonly performed filtering procedure is a trabeculectomy. In a trabeculectomy, a posterior incision is made in the conjunctiva, the transparent tissue that covers the sclera. The conjunctiva is rolled forward, exposing the sclera at the limbus. A partial thickness scleral flap is made and dissected half-thickness into the cornea. The anterior chamber is entered beneath the scleral flap and a section of deep sclera and trabecular meshwork is excised. The scleral flap is loosely sewn back into place. The conjunctival incision is tightly closed. Post-operatively, the aqueous fluid passes through the hole, beneath the scleral flap and collects in an elevated space beneath the conjunctiva. The fluid then is either absorbed through blood vessels in the conjunctiva or traverses across the conjunctiva into the tear film.
Trabeculectomy is associated with many problems. Fibroblasts that are present in the episclera proliferate and migrate and can scar down the scleral flap. Failure from scarring may occur, particularly in children and young adults. Of eyes that have an initially successful trabeculectomy, eighty percent will fail from scarring within three to five years after surgery. To minimize fibrosis, surgeons now are applying antifibrotic agents such as mitomycin C (MMC) and 5-fluorouracil (5-FU) to the scleral flap at the time of surgery. The use of these agents has increased the success rate of trabeculectomy but also has increased the prevalence of hypotony. Hypotony is a problem that develops when aqueous flows out of the eye too fast. The eye pressure drops too low (usually less than 6.0 mmHg); the structure of the eye collapses and vision decreases.
An alternative surgical method for glaucoma management can be directed more specifally at Schlemm""s canal. U.S. Pat. No. 5,360,399 teaches the placement of part of a plastic or steel tube into Schlemm""s canal with injection of a viscous material through holes in the tube to hydraulically hydrodissect the trabecular meshwork. However, the ""399 device provides little or no option for the distance of the hydrodissection within the length of Schlemm""s canal, nor suggests a means for dilating the canal to facilitate the natural drainage therefrom.
A need exists, then, for a system that would allow for precise dilation and expansion of Schlemm""s canal along any portion thereof. A need exists for the selective, direct delivery of therapeutic agents into Schlemm""s canal that provides more effective control of glaucoma with fewer systemic complications than with existing medication delivery alternatives. In addition, a more physiologic system is needed to enhance the drainage of aqueous fluid into Schlemm""s canal from the anterior chamber angle. Enhancing aqueous flow directly into Schlemm""s canal would minimize scarring since the angle region is populated with a single line of nonproliferating trabecular cells. Enhancing aqueous flow directly into Schlemm""s canal and naturally therefrom into the collecting channels would minimize hypotony since the canal is part of the normal outflow system and is biologically engineered to handle the normal volume of aqueous humor. Enhancing aqueous flow directly into Schlemm""s canal would eliminate complications such as endophthalmitis, hypotony, and leaks.
The present invention is directed to a novel inflatable catheter device and an associated method for the surgical correction of glaucoma in which the inventive device is placed within Schlemm""s canal and the inflatable element of the device is expanded to temporarily stretch and expand the lumen of the canal. At that point, the inflatable element may be used to temporarily occlude outflow through the canal, while physiologic material is injected through another lumen of the device, thereby distending the canal and expanding areas of stenosis within the canal. The inflated element may be decompressed and removed after the desired expansion is achieved, or the device may be extracted with the inflatable component expanded, to further mechanically dilate the passageway within Schlemm""s canal.
The present invention may also be employed to inject various medications directly within Schlemm""s canal. Such medications may include, but are not limited to, antifibrotics, antibiotics, and other medications which may have direct effects within the internal structures of Schlemm""s canal, the trabecular meshwork, and other tissues of the eye.
The present invention may also be employed to deploy various stents or shunts directly within Schlemm""s canal to help maintain patency within the canal following removal of the inflatable device.
The inventive device and method described herein therefore facilitates the normal physiologic pathway for drainage of aqueous humor from the anterior chamber to Schlemm""s canal and exiting to the collecting channels, rather than shunting to the sclera or another anatomic site as is done in most prior art devices. In addition, the present invention provides a mechanism for the delivery of devices or medications directly into Schlemm""s canal and the adjacent ophthalmic anatomy.